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<h1>Penlight</h1>

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  <li><a href="https://github.com/lunarmodules/Penlight">GitHub Project</a></li>
  <li><a href="../index.html">Documentation</a></li>
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<h2>Contents</h2>
<ul>
<li><a href="#Functions">Functions</a></li>
<li><a href="#Tables">Tables</a></li>
<li><a href="#Error_handling">Error handling </a></li>
<li><a href="#File_handling">File handling </a></li>
<li><a href="#OS_functions">OS functions </a></li>
<li><a href="#String_functions">String functions </a></li>
<li><a href="#Functional">Functional </a></li>
<li><a href="#Deprecation">Deprecation </a></li>
</ul>


<h2>Libraries</h2>
<ul class="nowrap">
  <li><a href="../libraries/pl.html">pl</a></li>
  <li><a href="../libraries/pl.app.html">pl.app</a></li>
  <li><a href="../libraries/pl.array2d.html">pl.array2d</a></li>
  <li><a href="../libraries/pl.class.html">pl.class</a></li>
  <li><a href="../libraries/pl.compat.html">pl.compat</a></li>
  <li><a href="../libraries/pl.comprehension.html">pl.comprehension</a></li>
  <li><a href="../libraries/pl.config.html">pl.config</a></li>
  <li><a href="../libraries/pl.data.html">pl.data</a></li>
  <li><a href="../libraries/pl.dir.html">pl.dir</a></li>
  <li><a href="../libraries/pl.file.html">pl.file</a></li>
  <li><a href="../libraries/pl.func.html">pl.func</a></li>
  <li><a href="../libraries/pl.import_into.html">pl.import_into</a></li>
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  <li><a href="../libraries/pl.luabalanced.html">pl.luabalanced</a></li>
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  <li><a href="../libraries/pl.test.html">pl.test</a></li>
  <li><a href="../libraries/pl.text.html">pl.text</a></li>
  <li><a href="../libraries/pl.types.html">pl.types</a></li>
  <li><a href="../libraries/pl.url.html">pl.url</a></li>
  <li><strong>pl.utils</strong></li>
  <li><a href="../libraries/pl.xml.html">pl.xml</a></li>
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<h2>Classes</h2>
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  <li><a href="../classes/pl.Date.html">pl.Date</a></li>
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<h2>Manual</h2>
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  <li><a href="../manual/01-introduction.md.html">Introduction</a></li>
  <li><a href="../manual/02-arrays.md.html">Tables and Arrays</a></li>
  <li><a href="../manual/03-strings.md.html">Strings. Higher-level operations on strings.</a></li>
  <li><a href="../manual/04-paths.md.html">Paths and Directories</a></li>
  <li><a href="../manual/05-dates.md.html">Date and Time</a></li>
  <li><a href="../manual/06-data.md.html">Data</a></li>
  <li><a href="../manual/07-functional.md.html">Functional Programming</a></li>
  <li><a href="../manual/08-additional.md.html">Additional Libraries</a></li>
  <li><a href="../manual/09-discussion.md.html">Technical Choices</a></li>
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<h2>Examples</h2>
<ul class="nowrap">
  <li><a href="../examples/seesubst.lua.html">seesubst.lua</a></li>
  <li><a href="../examples/sipscan.lua.html">sipscan.lua</a></li>
  <li><a href="../examples/symbols.lua.html">symbols.lua</a></li>
  <li><a href="../examples/test-cmp.lua.html">test-cmp.lua</a></li>
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  <li><a href="../examples/testxml.lua.html">testxml.lua</a></li>
  <li><a href="../examples/which.lua.html">which.lua</a></li>
</ul>

</div>

<div id="content">

<h1>Module <code>pl.utils</code></h1>
<p>Generally useful routines.</p>
<p> See  <a href="../manual/01-introduction.md.html#Generally_useful_functions_">the Guide</a>.</p>

<p> Dependencies: <a href="../libraries/pl.compat.html#">pl.compat</a>, all exported fields and functions from
 <a href="../libraries/pl.compat.html#">pl.compat</a> are also available in this module.</p>


<h2><a href="#Functions">Functions</a></h2>
<table class="function_list">
	<tr>
	<td class="name" nowrap><a href="#pack">pack (...)</a></td>
	<td class="summary">pack an argument list into a table.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#unpack">unpack (t[, i[, j]])</a></td>
	<td class="summary">unpack a table and return its contents.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#printf">printf (fmt, ...)</a></td>
	<td class="summary">print an arbitrary number of arguments using a format.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#fprintf">fprintf (f, fmt, ...)</a></td>
	<td class="summary">write an arbitrary number of arguments to a file using a format.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#import">import (t, T)</a></td>
	<td class="summary">take a table and 'inject' it into the local namespace.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#choose">choose (cond, value1, value2)</a></td>
	<td class="summary">return either of two values, depending on a condition.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#array_tostring">array_tostring (t[, temp[, tostr]])</a></td>
	<td class="summary">convert an array of values to strings.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#is_type">is_type (obj, tp)</a></td>
	<td class="summary">is the object of the specified type?</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#npairs">npairs (t[, i_start=1[, i_end=t.n or #t[, step=1]]])</a></td>
	<td class="summary">an iterator with indices, similar to <a href="https://www.lua.org/manual/5.4/manual.html#pdf-ipairs">ipairs</a>, but with a range.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#kpairs">kpairs (t)</a></td>
	<td class="summary">an iterator over all non-integer keys (inverse of <a href="https://www.lua.org/manual/5.4/manual.html#pdf-ipairs">ipairs</a>).</td>
	</tr>
</table>
<h2><a href="#Tables">Tables</a></h2>
<table class="function_list">
	<tr>
	<td class="name" nowrap><a href="#patterns">patterns</a></td>
	<td class="summary">Some standard patterns</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#stdmt">stdmt</a></td>
	<td class="summary">Standard meta-tables as used by other Penlight modules</td>
	</tr>
</table>
<h2><a href="#Error_handling">Error handling </a></h2>
<table class="function_list">
	<tr>
	<td class="name" nowrap><a href="#assert_arg">assert_arg (n, val, tp, verify, msg, lev)</a></td>
	<td class="summary">assert that the given argument is in fact of the correct type.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#enum">enum (...)</a></td>
	<td class="summary">creates an Enum or constants lookup table for improved error handling.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#function_arg">function_arg (idx, f, msg)</a></td>
	<td class="summary">process a function argument.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#assert_string">assert_string (n, val)</a></td>
	<td class="summary">assert the common case that the argument is a string.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#on_error">on_error (mode)</a></td>
	<td class="summary">control the error strategy used by Penlight.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#raise">raise (err)</a></td>
	<td class="summary">used by Penlight functions to return errors.</td>
	</tr>
</table>
<h2><a href="#File_handling">File handling </a></h2>
<table class="function_list">
	<tr>
	<td class="name" nowrap><a href="#readfile">readfile (filename, is_bin)</a></td>
	<td class="summary">return the contents of a file as a string</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#writefile">writefile (filename, str, is_bin)</a></td>
	<td class="summary">write a string to a file</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#readlines">readlines (filename)</a></td>
	<td class="summary">return the contents of a file as a list of lines</td>
	</tr>
</table>
<h2><a href="#OS_functions">OS functions </a></h2>
<table class="function_list">
	<tr>
	<td class="name" nowrap><a href="#executeex">executeex (cmd, bin)</a></td>
	<td class="summary">execute a shell command and return the output.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#quote_arg">quote_arg (argument)</a></td>
	<td class="summary">Quote and escape an argument of a command.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#quit">quit ([code], msg, ...)</a></td>
	<td class="summary">error out of this program gracefully.</td>
	</tr>
</table>
<h2><a href="#String_functions">String functions </a></h2>
<table class="function_list">
	<tr>
	<td class="name" nowrap><a href="#escape">escape (s)</a></td>
	<td class="summary">escape any Lua 'magic' characters in a string</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#split">split (s, re, plain, n)</a></td>
	<td class="summary">split a string into a list of strings separated by a delimiter.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#splitv">splitv (s, re, plain, n)</a></td>
	<td class="summary">split a string into a number of return values.</td>
	</tr>
</table>
<h2><a href="#Functional">Functional </a></h2>
<table class="function_list">
	<tr>
	<td class="name" nowrap><a href="#memoize">memoize (func)</a></td>
	<td class="summary">'memoize' a function (cache returned value for next call).</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#add_function_factory">add_function_factory (mt, fun)</a></td>
	<td class="summary">associate a function factory with a type.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#string_lambda">string_lambda (lf)</a></td>
	<td class="summary">an anonymous function as a string.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#bind1">bind1 (fn, p)</a></td>
	<td class="summary">bind the first argument of the function to a value.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#bind2">bind2 (fn, p)</a></td>
	<td class="summary">bind the second argument of the function to a value.</td>
	</tr>
</table>
<h2><a href="#Deprecation">Deprecation </a></h2>
<table class="function_list">
	<tr>
	<td class="name" nowrap><a href="#set_deprecation_func">set_deprecation_func (func)</a></td>
	<td class="summary">Sets a deprecation warning function.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#raise_deprecation">raise_deprecation (opts)</a></td>
	<td class="summary">raises a deprecation warning.</td>
	</tr>
</table>

<br/>
<br/>


    <h2 class="section-header "><a name="Functions"></a>Functions</h2>

    <dl class="function">
    <dt>
    <a name = "pack"></a>
    <strong>pack (...)</strong>
    </dt>
    <dd>
    pack an argument list into a table.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">...</span>
         any arguments
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        a table with field <code>n</code> set to the length
    </ol>


    <h3>See also:</h3>
    <ul>
         <li><a href="../libraries/pl.compat.html#table.pack">compat.pack</a></li>
         <li><a href="../libraries/pl.utils.html#npairs">utils.npairs</a></li>
         <li><a href="../libraries/pl.utils.html#unpack">utils.unpack</a></li>
    </ul>


</dd>
    <dt>
    <a name = "unpack"></a>
    <strong>unpack (t[, i[, j]])</strong>
    </dt>
    <dd>
    unpack a table and return its contents. </p>

<p> NOTE: this implementation differs from the Lua implementation in the way
 that this one DOES honor the <code>n</code> field in the table <code>t</code>, such that it is 'nil-safe'.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">t</span>
         table to unpack
        </li>
        <li><span class="parameter">i</span>
         index from which to start unpacking, defaults to 1
         (<em>optional</em>)
        </li>
        <li><span class="parameter">j</span>
         index of the last element to unpack, defaults to <code>t.n</code> or else <code>#t</code>
         (<em>optional</em>)
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        multiple return values from the table
    </ol>


    <h3>See also:</h3>
    <ul>
         <li><a href="../libraries/pl.compat.html#table.unpack">compat.unpack</a></li>
         <li><a href="../libraries/pl.utils.html#pack">utils.pack</a></li>
         <li><a href="../libraries/pl.utils.html#npairs">utils.npairs</a></li>
    </ul>

    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="keyword">local</span> t = <span class="global">table</span>.<span class="function-name">pack</span>(<span class="keyword">nil</span>, <span class="keyword">nil</span>, <span class="keyword">nil</span>, <span class="number">4</span>)
<span class="keyword">local</span> a, b, c, d = <span class="global">table</span>.<span class="function-name">unpack</span>(t)   <span class="comment">-- this <a href="../libraries/pl.utils.html#unpack">unpack</a> is NOT nil-safe, so d == nil
</span>
<span class="keyword">local</span> a, b, c, d = utils.<span class="function-name">unpack</span>(t)   <span class="comment">-- this is nil-safe, so d == 4</span></pre>
    </ul>

</dd>
    <dt>
    <a name = "printf"></a>
    <strong>printf (fmt, ...)</strong>
    </dt>
    <dd>
    print an arbitrary number of arguments using a format.
 Output will be sent to <code>stdout</code>.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">fmt</span>
         The format (see <a href="https://www.lua.org/manual/5.4/manual.html#pdf-string.format">string.format</a>)
        </li>
        <li><span class="parameter">...</span>
         Extra arguments for format
        </li>
    </ul>





</dd>
    <dt>
    <a name = "fprintf"></a>
    <strong>fprintf (f, fmt, ...)</strong>
    </dt>
    <dd>
    write an arbitrary number of arguments to a file using a format.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">f</span>
         File handle to write to.
        </li>
        <li><span class="parameter">fmt</span>
         The format (see <a href="https://www.lua.org/manual/5.4/manual.html#pdf-string.format">string.format</a>).
        </li>
        <li><span class="parameter">...</span>
         Extra arguments for format
        </li>
    </ul>





</dd>
    <dt>
    <a name = "import"></a>
    <strong>import (t, T)</strong>
    </dt>
    <dd>
    take a table and 'inject' it into the local namespace.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">t</span>
         The table (table), or module name (string), defaults to this <a href="../libraries/pl.utils.html">utils</a> module table
        </li>
        <li><span class="parameter">T</span>
         An optional destination table (defaults to callers environment)
        </li>
    </ul>





</dd>
    <dt>
    <a name = "choose"></a>
    <strong>choose (cond, value1, value2)</strong>
    </dt>
    <dd>
    return either of two values, depending on a condition.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">cond</span>
         A condition
        </li>
        <li><span class="parameter">value1</span>
         Value returned if cond is truthy
        </li>
        <li><span class="parameter">value2</span>
         Value returned if cond is falsy
        </li>
    </ul>





</dd>
    <dt>
    <a name = "array_tostring"></a>
    <strong>array_tostring (t[, temp[, tostr]])</strong>
    </dt>
    <dd>
    convert an array of values to strings.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">t</span>
         a list-like table
        </li>
        <li><span class="parameter">temp</span>
         (table) buffer to use, otherwise allocate
         (<em>optional</em>)
        </li>
        <li><span class="parameter">tostr</span>
         custom tostring function, called with (value,index). Defaults to <a href="https://www.lua.org/manual/5.4/manual.html#pdf-tostring">tostring</a>.
         (<em>optional</em>)
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        the converted buffer
    </ol>




</dd>
    <dt>
    <a name = "is_type"></a>
    <strong>is_type (obj, tp)</strong>
    </dt>
    <dd>
    is the object of the specified type?
 If the type is a string, then use type, otherwise compare with metatable


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">obj</span>
         An object to check
        </li>
        <li><span class="parameter">tp</span>
         String of what type it should be
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        boolean
    </ol>



    <h3>Usage:</h3>
    <ul>
        <pre class="example">utils.<span class="function-name">is_type</span>(<span class="string">"hello world"</span>, <span class="string">"string"</span>)   <span class="comment">--&gt; true
</span><span class="comment">-- or check metatable
</span><span class="keyword">local</span> my_mt = {}
<span class="keyword">local</span> my_obj = <span class="global">setmetatable</span>(my_obj, my_mt)
utils.<span class="function-name">is_type</span>(my_obj, my_mt)  <span class="comment">--&gt; true</span></pre>
    </ul>

</dd>
    <dt>
    <a name = "npairs"></a>
    <strong>npairs (t[, i_start=1[, i_end=t.n or #t[, step=1]]])</strong>
    </dt>
    <dd>
    an iterator with indices, similar to <a href="https://www.lua.org/manual/5.4/manual.html#pdf-ipairs">ipairs</a>, but with a range.
 This is a nil-safe index based iterator that will return <code>nil</code> when there
 is a hole in a list. To be safe ensure that table <code>t.n</code> contains the length.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">t</span>
            <span class="types"><a class="type" href="https://www.lua.org/manual/5.4/manual.html#6.6">table</a></span>
         the table to iterate over
        </li>
        <li><span class="parameter">i_start</span>
            <span class="types"><span class="type">integer</span></span>
         start index
         (<em>default</em> 1)
        </li>
        <li><span class="parameter">i_end</span>
            <span class="types"><span class="type">integer</span></span>
         end index
         (<em>default</em> t.n or #t)
        </li>
        <li><span class="parameter">step</span>
            <span class="types"><span class="type">integer</span></span>
         step size
         (<em>default</em> 1)
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>
        <li>
           <span class="types"><span class="type">integer</span></span>
        index</li>
        <li>
           <span class="types"><span class="type">any</span></span>
        value at index (which can be <code>nil</code>!)</li>
    </ol>


    <h3>See also:</h3>
    <ul>
         <li><a href="../libraries/pl.utils.html#pack">utils.pack</a></li>
         <li><a href="../libraries/pl.utils.html#unpack">utils.unpack</a></li>
    </ul>

    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="keyword">local</span> t = utils.<span class="function-name">pack</span>(<span class="keyword">nil</span>, <span class="number">123</span>, <span class="keyword">nil</span>)  <span class="comment">-- adds an <code>n</code> field when packing
</span>
<span class="keyword">for</span> i, v <span class="keyword">in</span> utils.<span class="function-name">npairs</span>(t, <span class="number">2</span>) <span class="keyword">do</span>  <span class="comment">-- start at index 2
</span>  t[i] = <span class="global">tostring</span>(t[i])
<span class="keyword">end</span>

<span class="comment">-- t = { n = 3, [2] = "123", [3] = "nil" }</span></pre>
    </ul>

</dd>
    <dt>
    <a name = "kpairs"></a>
    <strong>kpairs (t)</strong>
    </dt>
    <dd>
    an iterator over all non-integer keys (inverse of <a href="https://www.lua.org/manual/5.4/manual.html#pdf-ipairs">ipairs</a>).
 It will skip any key that is an integer number, so negative indices or an
 array with holes will not return those either (so it returns slightly less than
 'the inverse of <a href="https://www.lua.org/manual/5.4/manual.html#pdf-ipairs">ipairs</a>').</p>

<p> This uses <a href="https://www.lua.org/manual/5.4/manual.html#pdf-pairs">pairs</a> under the hood, so any value that is iterable using <a href="https://www.lua.org/manual/5.4/manual.html#pdf-pairs">pairs</a>
 will work with this function.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">t</span>
            <span class="types"><a class="type" href="https://www.lua.org/manual/5.4/manual.html#6.6">table</a></span>
         the table to iterate over
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>
        <li>
           <span class="types"><span class="type">key</span></span>


</li>
        <li>
           <span class="types"><span class="type">value</span></span>


</li>
    </ol>



    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="keyword">local</span> t = {
  <span class="string">"hello"</span>,
  <span class="string">"world"</span>,
  hello = <span class="string">"hallo"</span>,
  world = <span class="string">"Welt"</span>,
}

<span class="keyword">for</span> k, v <span class="keyword">in</span> utils.<span class="function-name">kpairs</span>(t) <span class="keyword">do</span>
  <span class="global">print</span>(<span class="string">"German: "</span>, v)
<span class="keyword">end</span>

<span class="comment">-- output;
</span><span class="comment">-- German: hallo
</span><span class="comment">-- German: Welt</span></pre>
    </ul>

</dd>
</dl>
    <h2 class="section-header "><a name="Tables"></a>Tables</h2>

    <dl class="function">
    <dt>
    <a name = "patterns"></a>
    <strong>patterns</strong>
    </dt>
    <dd>
    Some standard patterns


    <h3>Fields:</h3>
    <ul>
        <li><span class="parameter">FLOAT</span>
        floating point number
        </li>
        <li><span class="parameter">INTEGER</span>
        integer number
        </li>
        <li><span class="parameter">IDEN</span>
        identifier
        </li>
        <li><span class="parameter">FILE</span>
        file
        </li>
    </ul>





</dd>
    <dt>
    <a name = "stdmt"></a>
    <strong>stdmt</strong>
    </dt>
    <dd>
    Standard meta-tables as used by other Penlight modules


    <h3>Fields:</h3>
    <ul>
        <li><span class="parameter">List</span>
         the List metatable
        </li>
        <li><span class="parameter">Map</span>
         the Map metatable
        </li>
        <li><span class="parameter">Set</span>
         the Set metatable
        </li>
        <li><span class="parameter">MultiMap</span>
         the MultiMap metatable
        </li>
    </ul>





</dd>
</dl>
    <h2 class="section-header "><a name="Error_handling"></a>Error handling </h2>

    <dl class="function">
    <dt>
    <a name = "assert_arg"></a>
    <strong>assert_arg (n, val, tp, verify, msg, lev)</strong>
    </dt>
    <dd>
    assert that the given argument is in fact of the correct type.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">n</span>
         argument index
        </li>
        <li><span class="parameter">val</span>
         the value
        </li>
        <li><span class="parameter">tp</span>
         the type
        </li>
        <li><span class="parameter">verify</span>
         an optional verification function
        </li>
        <li><span class="parameter">msg</span>
         an optional custom message
        </li>
        <li><span class="parameter">lev</span>
         optional stack position for trace, default 2
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        the validated value
    </ol>

    <h3>Raises:</h3>
    if <code>val</code> is not the correct type


    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="keyword">local</span> param1 = <span class="function-name">assert_arg</span>(<span class="number">1</span>,<span class="string">"hello"</span>,<span class="string">'table'</span>)  <span class="comment">--&gt; error: argument 1 expected a 'table', got a 'string'
</span><span class="keyword">local</span> param4 = <span class="function-name">assert_arg</span>(<span class="number">4</span>,<span class="string">'!@#$%^&amp;*'</span>,<span class="string">'string'</span>,path.isdir,<span class="string">'not a directory'</span>)
     <span class="comment">--&gt; error: argument 4: '!@#$%^&amp;*' not a directory</span></pre>
    </ul>

</dd>
    <dt>
    <a name = "enum"></a>
    <strong>enum (...)</strong>
    </dt>
    <dd>
    creates an Enum or constants lookup table for improved error handling.
 This helps prevent magic strings in code by throwing errors for accessing
 non-existing values, and/or converting strings/identifiers to other values.</p>

<p> Calling on the object does the same, but returns a soft error; <code>nil + err</code>, if
 the call is successful (the key exists), it will return the value.</p>

<p> When calling with varargs or an array the values will be equal to the keys.
 The enum object is read-only.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">...</span>
            <span class="types"><a class="type" href="https://www.lua.org/manual/5.4/manual.html#6.6">table</a> or <span class="type">vararg</span></span>
         the input for the Enum. If varargs or an array then the
 values in the Enum will be equal to the names (must be strings), if a hash-table
 then values remain (any type), and the keys must be strings.
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        Enum object (read-only table/object)
    </ol>



    <h3>Usage:</h3>
    <ul>
        <li><pre class="example"><span class="comment">-- Enum access at runtime
</span><span class="keyword">local</span> obj = {}
obj.MOVEMENT = utils.<span class="function-name">enum</span>(<span class="string">"FORWARD"</span>, <span class="string">"REVERSE"</span>, <span class="string">"LEFT"</span>, <span class="string">"RIGHT"</span>)

<span class="keyword">if</span> current_movement == obj.MOVEMENT.FORWARD <span class="keyword">then</span>
  <span class="comment">-- do something
</span>
<span class="keyword">elseif</span> current_movement == obj.MOVEMENT.REVERES <span class="keyword">then</span>
  <span class="comment">-- throws error due to typo 'REVERES', so a silent mistake becomes a hard error
</span>  <span class="comment">-- "'REVERES' is not a valid value (expected one of: 'FORWARD', 'REVERSE', 'LEFT', 'RIGHT')"
</span>
<span class="keyword">end</span></pre></li>
        <li><pre class="example"><span class="comment">-- standardized error codes
</span><span class="keyword">local</span> obj = {
  ERR = utils.<span class="function-name">enum</span> {
    NOT_FOUND = <span class="string">"the item was not found"</span>,
    OUT_OF_BOUNDS = <span class="string">"the index is outside the allowed range"</span>
  },

  some_method = <span class="keyword">function</span>(self)
    <span class="keyword">return</span> <span class="keyword">nil</span>, self.ERR.OUT_OF_BOUNDS
  <span class="keyword">end</span>,
}

<span class="keyword">local</span> result, err = obj:<span class="function-name">some_method</span>()
<span class="keyword">if</span> <span class="keyword">not</span> result <span class="keyword">then</span>
  <span class="keyword">if</span> err == obj.ERR.NOT_FOUND <span class="keyword">then</span>
    <span class="comment">-- check on error code, not magic strings
</span>
  <span class="keyword">else</span>
    <span class="comment">-- return the error description, contained in the constant
</span>    <span class="keyword">return</span> <span class="keyword">nil</span>, <span class="string">"error: "</span>..err  <span class="comment">-- "error: the index is outside the allowed range"
</span>  <span class="keyword">end</span>
<span class="keyword">end</span></pre></li>
        <li><pre class="example"><span class="comment">-- validating/converting user-input
</span><span class="keyword">local</span> color = <span class="string">"purple"</span>
<span class="keyword">local</span> ansi_colors = utils.<span class="function-name">enum</span> {
  black     = <span class="number">30</span>,
  red       = <span class="number">31</span>,
  green     = <span class="number">32</span>,
}
<span class="keyword">local</span> color_code, err = <span class="function-name">ansi_colors</span>(color) <span class="comment">-- calling on the object, returns the value from the enum
</span><span class="keyword">if</span> <span class="keyword">not</span> color_code <span class="keyword">then</span>
  <span class="global">print</span>(<span class="string">"bad 'color', "</span> .. err)
  <span class="comment">-- "bad 'color', 'purple' is not a valid value (expected one of: 'black', 'red', 'green')"
</span>  <span class="global">os</span>.<span class="function-name">exit</span>(<span class="number">1</span>)
<span class="keyword">end</span></pre></li>
    </ul>

</dd>
    <dt>
    <a name = "function_arg"></a>
    <strong>function_arg (idx, f, msg)</strong>
    </dt>
    <dd>
    process a function argument.
 This is used throughout Penlight and defines what is meant by a function:
 Something that is callable, or an operator string as defined by <code>pl.operator</code>,
 such as '>' or '#'. If a function factory has been registered for the type, it will
 be called to get the function.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">idx</span>
         argument index
        </li>
        <li><span class="parameter">f</span>
         a function, operator string, or callable object
        </li>
        <li><span class="parameter">msg</span>
         optional error message
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        a callable
    </ol>

    <h3>Raises:</h3>
    if idx is not a number or if f is not callable



</dd>
    <dt>
    <a name = "assert_string"></a>
    <strong>assert_string (n, val)</strong>
    </dt>
    <dd>
    assert the common case that the argument is a string.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">n</span>
         argument index
        </li>
        <li><span class="parameter">val</span>
         a value that must be a string
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        the validated value
    </ol>

    <h3>Raises:</h3>
    val must be a string


    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="keyword">local</span> val = <span class="number">42</span>
<span class="keyword">local</span> param2 = utils.<span class="function-name">assert_string</span>(<span class="number">2</span>, val) <span class="comment">--&gt; error: argument 2 expected a 'string', got a 'number'</span></pre>
    </ul>

</dd>
    <dt>
    <a name = "on_error"></a>
    <strong>on_error (mode)</strong>
    </dt>
    <dd>

<p>control the error strategy used by Penlight.
 This is a global setting that controls how <a href="../libraries/pl.utils.html#raise">utils.raise</a> behaves:</p>

<ul>
    <li>'default': return <code>nil + error</code> (this is the default)</li>
    <li>'error': throw a Lua error</li>
    <li>'quit': exit the program</li>
</ul>




    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">mode</span>
         either 'default', 'quit'  or 'error'
        </li>
    </ul>



    <h3>See also:</h3>
    <ul>
         <a href="../libraries/pl.utils.html#raise">utils.raise</a>
    </ul>


</dd>
    <dt>
    <a name = "raise"></a>
    <strong>raise (err)</strong>
    </dt>
    <dd>
    used by Penlight functions to return errors.  Its global behaviour is controlled
 by <a href="../libraries/pl.utils.html#on_error">utils.on_error</a>.
 To use this function you MUST use it in conjunction with <code>return</code>, since it might
 return <code>nil + error</code>.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">err</span>
         the error string.
        </li>
    </ul>



    <h3>See also:</h3>
    <ul>
         <a href="../libraries/pl.utils.html#on_error">utils.on_error</a>
    </ul>

    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="keyword">if</span> some_condition <span class="keyword">then</span>
  <span class="keyword">return</span> utils.<span class="function-name">raise</span>(<span class="string">"some condition was not met"</span>)  <span class="comment">-- MUST use 'return'!
</span><span class="keyword">end</span></pre>
    </ul>

</dd>
</dl>
    <h2 class="section-header "><a name="File_handling"></a>File handling </h2>

    <dl class="function">
    <dt>
    <a name = "readfile"></a>
    <strong>readfile (filename, is_bin)</strong>
    </dt>
    <dd>
    return the contents of a file as a string


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">filename</span>
         The file path
        </li>
        <li><span class="parameter">is_bin</span>
         open in binary mode
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        file contents
    </ol>




</dd>
    <dt>
    <a name = "writefile"></a>
    <strong>writefile (filename, str, is_bin)</strong>
    </dt>
    <dd>
    write a string to a file


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">filename</span>
         The file path
        </li>
        <li><span class="parameter">str</span>
         The string
        </li>
        <li><span class="parameter">is_bin</span>
         open in binary mode
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>
        <li>
        true or nil</li>
        <li>
        error message</li>
    </ol>

    <h3>Raises:</h3>
    error if filename or str aren't strings



</dd>
    <dt>
    <a name = "readlines"></a>
    <strong>readlines (filename)</strong>
    </dt>
    <dd>
    return the contents of a file as a list of lines


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">filename</span>
         The file path
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        file contents as a table
    </ol>

    <h3>Raises:</h3>
    error if filename is not a string



</dd>
</dl>
    <h2 class="section-header "><a name="OS_functions"></a>OS functions </h2>

    <dl class="function">
    <dt>
    <a name = "executeex"></a>
    <strong>executeex (cmd, bin)</strong>
    </dt>
    <dd>
    execute a shell command and return the output.
 This function redirects the output to tempfiles and returns the content of those files.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">cmd</span>
         a shell command
        </li>
        <li><span class="parameter">bin</span>
         boolean, if true, read output as binary file
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>
        <li>
        true if successful</li>
        <li>
        actual return code</li>
        <li>
        stdout output (string)</li>
        <li>
        errout output (string)</li>
    </ol>




</dd>
    <dt>
    <a name = "quote_arg"></a>
    <strong>quote_arg (argument)</strong>
    </dt>
    <dd>
    Quote and escape an argument of a command.
 Quotes a single (or list of) argument(s) of a command to be passed
 to <a href="https://www.lua.org/manual/5.4/manual.html#pdf-os.execute">os.execute</a>, <code>pl.utils.execute</code> or <a href="../libraries/pl.utils.html#executeex">pl.utils.executeex</a>.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">argument</span>
         (string or table/list) the argument to quote. If a list then
 all arguments in the list will be returned as a single string quoted.
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        quoted and escaped argument.
    </ol>



    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="keyword">local</span> options = utils.<span class="function-name">quote_arg</span> {
    <span class="string">"-lluacov"</span>,
    <span class="string">"-e"</span>,
    <span class="string">"utils = print(require('pl.utils')._VERSION"</span>,
}
<span class="comment">-- returns: -lluacov -e 'utils = print(require('\''pl.utils'\'')._VERSION'</span></pre>
    </ul>

</dd>
    <dt>
    <a name = "quit"></a>
    <strong>quit ([code], msg, ...)</strong>
    </dt>
    <dd>
    error out of this program gracefully.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">code</span>
         The exit code, defaults to -<code>1</code> if omitted
         (<em>optional</em>)
        </li>
        <li><span class="parameter">msg</span>
         The exit message will be sent to <code>stderr</code> (will be formatted with the extra parameters)
        </li>
        <li><span class="parameter">...</span>
         extra arguments for message's format'
        </li>
    </ul>



    <h3>See also:</h3>
    <ul>
         <a href="../libraries/pl.utils.html#fprintf">utils.fprintf</a>
    </ul>

    <h3>Usage:</h3>
    <ul>
        <pre class="example">utils.<span class="function-name">quit</span>(-<span class="number">1</span>, <span class="string">"Error '%s' happened"</span>, <span class="string">"42"</span>)
<span class="comment">-- is equivalent to
</span>utils.<span class="function-name">quit</span>(<span class="string">"Error '%s' happened"</span>, <span class="string">"42"</span>)  <span class="comment">--&gt; Error '42' happened</span></pre>
    </ul>

</dd>
</dl>
    <h2 class="section-header "><a name="String_functions"></a>String functions </h2>

    <dl class="function">
    <dt>
    <a name = "escape"></a>
    <strong>escape (s)</strong>
    </dt>
    <dd>
    escape any Lua 'magic' characters in a string


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">s</span>
         The input string
        </li>
    </ul>





</dd>
    <dt>
    <a name = "split"></a>
    <strong>split (s, re, plain, n)</strong>
    </dt>
    <dd>
    split a string into a list of strings separated by a delimiter.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">s</span>
         The input string
        </li>
        <li><span class="parameter">re</span>
         optional A Lua string pattern; defaults to '%s+'
        </li>
        <li><span class="parameter">plain</span>
         optional If truthy don't use Lua patterns
        </li>
        <li><span class="parameter">n</span>
         optional maximum number of elements (if there are more, the last will remain un-split)
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        a list-like table
    </ol>

    <h3>Raises:</h3>
    error if s is not a string

    <h3>See also:</h3>
    <ul>
         <a href="../libraries/pl.utils.html#splitv">splitv</a>
    </ul>


</dd>
    <dt>
    <a name = "splitv"></a>
    <strong>splitv (s, re, plain, n)</strong>
    </dt>
    <dd>
    split a string into a number of return values.
 Identical to <a href="../libraries/pl.utils.html#split">split</a> but returns multiple sub-strings instead of
 a single list of sub-strings.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">s</span>
         the string
        </li>
        <li><span class="parameter">re</span>
         A Lua string pattern; defaults to '%s+'
        </li>
        <li><span class="parameter">plain</span>
         don't use Lua patterns
        </li>
        <li><span class="parameter">n</span>
         optional maximum number of splits
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        n values
    </ol>


    <h3>See also:</h3>
    <ul>
         <a href="../libraries/pl.utils.html#split">split</a>
    </ul>

    <h3>Usage:</h3>
    <ul>
        <pre class="example">first,<span class="global">next</span> = <span class="function-name">splitv</span>(<span class="string">'user=jane=doe'</span>,<span class="string">'='</span>, <span class="keyword">false</span>, <span class="number">2</span>)
<span class="global">assert</span>(first == <span class="string">"user"</span>)
<span class="global">assert</span>(<span class="global">next</span> == <span class="string">"jane=doe"</span>)</pre>
    </ul>

</dd>
</dl>
    <h2 class="section-header "><a name="Functional"></a>Functional </h2>

    <dl class="function">
    <dt>
    <a name = "memoize"></a>
    <strong>memoize (func)</strong>
    </dt>
    <dd>
    'memoize' a function (cache returned value for next call).
 This is useful if you have a function which is relatively expensive,
 but you don't know in advance what values will be required, so
 building a table upfront is wasteful/impossible.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">func</span>
         a function that takes exactly one argument (which later serves as the cache key) and returns a single value
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        a function taking one argument and returning a single value either from the cache or by running the original input function
    </ol>




</dd>
    <dt>
    <a name = "add_function_factory"></a>
    <strong>add_function_factory (mt, fun)</strong>
    </dt>
    <dd>
    associate a function factory with a type.
 A function factory takes an object of the given type and
 returns a function for evaluating it


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">mt</span>
            <span class="types"><a class="type" href="https://www.lua.org/manual/5.4/manual.html#6.6">table</a></span>
         metatable
        </li>
        <li><span class="parameter">fun</span>
            <span class="types"><span class="type">function</span></span>
         a callable that returns a function
        </li>
    </ul>





</dd>
    <dt>
    <a name = "string_lambda"></a>
    <strong>string_lambda (lf)</strong>
    </dt>
    <dd>
    an anonymous function as a string.  This string is either of the form
 '|args| expression' or is a function of one argument, '_'


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">lf</span>
         function as a string
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        a function
    </ol>



    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="function-name">string_lambda</span> <span class="string">'|x|x+1'</span> (<span class="number">2</span>) == <span class="number">3</span>
<span class="function-name">string_lambda</span> <span class="string">'_+1'</span> (<span class="number">2</span>) == <span class="number">3</span></pre>
    </ul>

</dd>
    <dt>
    <a name = "bind1"></a>
    <strong>bind1 (fn, p)</strong>
    </dt>
    <dd>
    bind the first argument of the function to a value.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">fn</span>
         a function of at least two values (may be an operator string)
        </li>
        <li><span class="parameter">p</span>
         a value
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        a function such that f(x) is fn(p,x)
    </ol>

    <h3>Raises:</h3>
    same as <a href="../libraries/pl.utils.html#function_arg">function_arg</a>

    <h3>See also:</h3>
    <ul>
         <a href="../libraries/pl.func.html#bind1">func.bind1</a>
    </ul>

    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="keyword">local</span> <span class="keyword">function</span> <span class="function-name">f</span>(msg, name)
  <span class="global">print</span>(msg .. <span class="string">" "</span> .. name)
<span class="keyword">end</span>

<span class="keyword">local</span> hello = utils.<span class="function-name">bind1</span>(f, <span class="string">"Hello"</span>)

<span class="global">print</span>(<span class="function-name">hello</span>(<span class="string">"world"</span>))     <span class="comment">--&gt; "Hello world"
</span><span class="global">print</span>(<span class="function-name">hello</span>(<span class="string">"sunshine"</span>))  <span class="comment">--&gt; "Hello sunshine"</span></pre>
    </ul>

</dd>
    <dt>
    <a name = "bind2"></a>
    <strong>bind2 (fn, p)</strong>
    </dt>
    <dd>
    bind the second argument of the function to a value.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">fn</span>
         a function of at least two values (may be an operator string)
        </li>
        <li><span class="parameter">p</span>
         a value
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        a function such that f(x) is fn(x,p)
    </ol>

    <h3>Raises:</h3>
    same as <a href="../libraries/pl.utils.html#function_arg">function_arg</a>


    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="keyword">local</span> <span class="keyword">function</span> <span class="function-name">f</span>(a, b, c)
  <span class="global">print</span>(a .. <span class="string">" "</span> .. b .. <span class="string">" "</span> .. c)
<span class="keyword">end</span>

<span class="keyword">local</span> hello = utils.<span class="function-name">bind1</span>(f, <span class="string">"world"</span>)

<span class="global">print</span>(<span class="function-name">hello</span>(<span class="string">"Hello"</span>, <span class="string">"!"</span>))  <span class="comment">--&gt; "Hello world !"
</span><span class="global">print</span>(<span class="function-name">hello</span>(<span class="string">"Bye"</span>, <span class="string">"?"</span>))    <span class="comment">--&gt; "Bye world ?"</span></pre>
    </ul>

</dd>
</dl>
    <h2 class="section-header "><a name="Deprecation"></a>Deprecation </h2>

    <dl class="function">
    <dt>
    <a name = "set_deprecation_func"></a>
    <strong>set_deprecation_func (func)</strong>
    </dt>
    <dd>
    Sets a deprecation warning function.
 An application can override this function to support proper output of
 deprecation warnings. The warnings can be generated from libraries or
 functions by calling <a href="../libraries/pl.utils.html#raise_deprecation">utils.raise_deprecation</a>. The default function
 will write to the 'warn' system (introduced in Lua 5.4, or the compatibility
 function from the <a href="../libraries/pl.compat.html">compat</a> module for earlier versions).</p>

<p> Note: only applications should set/change this function, libraries should not.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">func</span>
         a callback with signature: <code>function(msg, trace)</code> both arguments are strings, the latter being optional.
        </li>
    </ul>



    <h3>See also:</h3>
    <ul>
         <a href="../libraries/pl.utils.html#raise_deprecation">utils.raise_deprecation</a>
    </ul>

    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="comment">-- write to the Nginx logs with OpenResty
</span>utils.<span class="function-name">set_deprecation_func</span>(<span class="keyword">function</span>(msg, trace)
  ngx.<span class="function-name">log</span>(ngx.WARN, msg, (trace <span class="keyword">and</span> (<span class="string">" "</span> .. trace) <span class="keyword">or</span> <span class="keyword">nil</span>))
<span class="keyword">end</span>)

<span class="comment">-- disable deprecation warnings
</span>utils.<span class="function-name">set_deprecation_func</span>()</pre>
    </ul>

</dd>
    <dt>
    <a name = "raise_deprecation"></a>
    <strong>raise_deprecation (opts)</strong>
    </dt>
    <dd>
    raises a deprecation warning.
 For options see the usage example below.</p>

<p> Note: the <code>opts.deprecated_after</code> field is the last version in which
 a feature or option was NOT YET deprecated! Because when writing the code it
 is quite often not known in what version the code will land. But the last
 released version is usually known.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">opts</span>
         options table
        </li>
    </ul>



    <h3>See also:</h3>
    <ul>
         <a href="../libraries/pl.utils.html#set_deprecation_func">utils.set_deprecation_func</a>
    </ul>

    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="global">warn</span>(<span class="string">"@on"</span>)   <span class="comment">-- enable Lua warnings, they are usually off by default
</span>
<span class="keyword">function</span> stringx.<span class="function-name">islower</span>(str)
  <span class="function-name">raise_deprecation</span> {
    source = <span class="string">"Penlight "</span> .. utils._VERSION,                   <span class="comment">-- optional
</span>    message = <span class="string">"function 'islower' was renamed to 'is_lower'"</span>, <span class="comment">-- required
</span>    version_removed = <span class="string">"2.0.0"</span>,                                <span class="comment">-- optional
</span>    deprecated_after = <span class="string">"1.2.3"</span>,                               <span class="comment">-- optional
</span>    no_trace = <span class="keyword">true</span>,                                          <span class="comment">-- optional
</span>  }
  <span class="keyword">return</span> stringx.<span class="function-name">is_lower</span>(str)
<span class="keyword">end</span>
<span class="comment">-- output: "[Penlight 1.9.2] function 'islower' was renamed to 'is_lower' (deprecated after 1.2.3, scheduled for removal in 2.0.0)"</span></pre>
    </ul>

</dd>
</dl>


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